In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), active studies are underway on standardization of a mobile communication standard to realize low-delay and high-speed transmission.
To realize low-delay and high-speed transmission, OFDM (Orthogonal Frequency Division Multiplexing) is adopted as a downlink (DL) multiple access scheme and SC-FDMA (Single-Carrier Frequency Division Multiple Access) using DFT (Discrete Fourier Transform) precoding is adopted as an uplink (UL) multiple access scheme.
SC-FDMA using DFT precoding uses a DFT matrix (precoding matrix or DFT sequence) represented by, for example, an N×N matrix. Here, N is the size of DFT (the number of DFT points). Furthermore, in an N×N DFT matrix, N (N×1) column vectors are orthogonal to each other in DFT size N. SC-FDMA using DFT precoding forms an SC-FDMA signal (spectrum) by spreading and code-multiplexing a symbol sequence using this DFT matrix.
Furthermore, standardization of LTE-Advanced (or IMT (International Mobile Telecommunication)-Advanced) to realize higher-speed communication than LTE has started. In LTE-Advanced, a radio communication base station apparatus (hereinafter referred to as “base station”) and a radio communication terminal apparatus (hereinafter referred to as “terminal”) which are communicable using a wideband of, for example, 40 MHz or higher are expected to be introduced to realize higher-speed communication.
As for an LTE uplink, uplink frequency resource allocation is limited to such allocation that SC-FDMA signals are mapped to continuous frequency bands in a localized manner to maintain single-carrier characteristics (e.g. low PAPR (Peak-to-Average Power Ratio) characteristics) of a transmission signal for realizing high coverage.
However, when frequency resource allocation is limited as described above, vacancy is produced in uplink shared frequency resources (e.g. PUSCH (Physical Uplink Shared CHannel)) and the efficiency of the use of frequency resources becomes worse. Thus, as a prior art for improving the efficiency of the use of frequency resources, clustered SC-FDMA (C-SC-FDMA) is proposed which divides an SC-FDMA signal into a plurality of clusters and maps the plurality of clusters to discontinuous frequency resources (e.g. see non-patent literature 1).
In C-SC-FDMA of the above prior art, a terminal generates C-SC-FDMA signals by dividing an SC-FDMA signal (spectrum) generated through DFT processing into a plurality of clusters. The terminal then maps the plurality of clusters to discontinuous frequency resources (subcarriers or resource blocks (RB)). On the other hand, a base station applies frequency domain equalization (FDE) processing to the received C-SC-FDMA signals (plurality of clusters) and combines the plurality of clusters after the equalization. The base station then applies IDFT (Inverse Discrete Fourier Transform) processing to the combined signal and thereby obtains a time domain signal.
C-SC-FDMA can allocate frequency resources among a plurality of terminals more flexibly than SC-FDMA by mapping the plurality of clusters to a plurality of discontinuous frequency resources, and can thereby improve the efficiency of the use of frequency resources and multiuser diversity effect. Furthermore, C-SC-FDMA has a smaller PAPR than that of OFDMA (Orthogonal Frequency Division Multiple Access), and can thereby expand uplink coverage more than OFDMA.
Furthermore, a C-SC-FDMA configuration can be easily realized by only adding a component that divides an SC-FDMA signal (spectrum) into a plurality of clusters to the terminal and adding a component that combines a plurality of clusters to the base station in the conventional SC-FDMA configuration.